抄録
The growth behaviour of microstructurally small fatigue cracks has been investigated with smooth specimens of a ferritic-pearlitic steel, S45C, under rotating bending. The effects of microstructure, particularly the roles of pearlite structure, on crack growth were evaluated based on detailed microscopic observations. In regions smaller than a certain crack length, cracks tended on grow preferentially in ferrite structure, and crack growth rates decreased markedly at ferritepearlite boundaries when cracks grew into pearlite structure from ferrite structure. The above region of crack length, i.e. the length of a microstructurally small crack, depended on stress level and increased with decreasing stress level. The growth mechanism is also discussed in terms of the results of fractography.
